1. Field of the Invention
The present invention relates generally to the field of robotics, and more particularly to hydraulically operated robot arms with spherical wrist joints and telescoping extension means.
2. Description of Related Art
Robotic arm mechanisms may be divided broadly into two major categories: 1), those that are operated with hydraulic actuators and 2), those that use other means, usually electric motors and various gearing or linkages or both. There are advantages and disadvantages to both approaches. Hydraulic solutions are very powerful in limited spaces but require seals to retain working fluids. Electric motor driven mechanisms usually don't have leakage problems but are relatively weak for a given size effector. Depending on the exact configuration, both hydraulic and electric approaches can suffer from significant singularity problems.
Singularities occur when the mechanism gets "twisted" and must make a high velocity movement of a particular joint mechanism to compensate for the twist and allow the end effector to follow a particular path and velocity. This problem was studied by Robert Y. Dien and Ethan C. Luce, and the results are presented in their U.S. Pat. No. 4,628,765 for a spherical robotic wrist joint. They conclude that singularities can be avoided if the various axes of rotation used coincide at a single point. One such configuration is a spherical joint.
The present invention is based on hydraulically actuated spherical joints so the background discussion is limited to similar hydraulically actuated mechanisms.
U.S. Pat. No. 3,973,469, issued to John Humen, shows a generally spherical floating chamber machine that might be back-driven with fluid pressure to effect a two-degree of freedom wrist joint.
U.S. Pat. No. 4,045,958, issued to William M. Wells, shows a generally spherical multi-directional positioner with two degrees of motion freedom that could be used as a robot wrist joint.
U.S. Pat. Nos. 4,194,437 and 4,296,681, issued to Mark E. Rosheim, show generally spherical hydraulic servo mechanisms with two degrees of freedom that could be used as a robot wrist joint.
Each of the above listed patents show devices that appear singularity-free within the range of their motions. However, some appear to be difficult to seal against leaks. All are limited to two degrees of motion freedom, albeit in different axes.